Fluid storage tanks are often utilized at fuel refilling stations and the like to store fluid for subsequent removal or dispensing. The storage tanks are typically refilled with fluid from an external source, such as a tanker truck. The tank may include an overfill prevention valve to prevent overfilling, which can help to prevent spills, reduce environmental damage and minimize loss of fluid. However, existing overfill prevention valves may not provide sufficient test functionality to ensure proper operation of the valve.